Explosion percussion machines with a freely running striking piston



Oct. 7, 1958 G. A. BERGMAN EXPLOSION 2,854,962 EELY PERCUSSION MACHINES WITH A FR RUNNING STRIKING PISTON Filed D90. :19, 1955 84% f0 3 Em w MW %4 IN VEN TOR.

PW W 9 PM I11! I in L Flyj v FJITIIU' United rates Patent 9 EXPLUSIQN PERQUSSHQN MACHINES WITH A FREELY RUNNHNG STRIKWG PESTON Gustav Albert Bergman, Danderyd, Sweden Application December 19, 1955, Serial No. 554,033 Claims priority, application Sweden May 17, 1955 3 (Ilairns. (Cl. 123- 7) The present invention refers to explosion percussion machines such as rock drilling machines or breaking tools with a free-floating striking or percussion piston provided with an auxiliary piston and running in a striking piston cylinder connected to or integral with the cylinder of an internal combustion engine. In machines of this type, the auxiliary piston defines on one side thereof a gas space in communication with the combustion chamber of the engine, a gas cushion being formed in said gas space, which cushion is called upon to return the striking piston, after the latter has hit the neck of the tool proper, i. e. of the drill, breaking chisel and the like, during a working stroke.

The gas cushion mostly operates satisfactorily, when the percussion machine is adapted for drilling, but particularly in breaking work, during which the entire machine is lifted repeatedly during work, so that the tool is brought out of touch with the ground or the work piece, certain serious drawbacks are sometimes met with. The walls surrounding the gas cushion, which are in a continuous contact with hot combustion gases, assume rather a high temperature, and the gas in the gas cushion also has a high temperature. When the striking piston approaches its extreme position during a working stroke, the temperature rises further on account of the compression of the gas. The gas space frequently contains some vaporized lubricating oil, when the striking piston and the surrounding Walls are lubricated with oil. The pressure and the temperature may then become so high in the gas cushion, where the gas most frequently mingles with air leaking into the same, that an explosion takes place, the striking piston being then thrown back into its inner (upper) extreme position with great force. The impetus of the movement may become so great that the striking piston strikes against the inner end Wall of the striking piston cylinder. The frequently repeated, very powerful blows against this end wall, which thus set in, lead to fatiguing of the material of the cylinder as well as of the striking piston, which causes fissures in the material and destruction in a relatively short time. Similar disadvantages may present themselves, if the striking piston is returned by means of compressed air.

Said drawbacks are obviated according to the invention by an arrangement adapted to restrict the pressure in the striking piston cylinder on the outside of the striking piston to a maximum value which is nevertheless higher than the pressure normally required to return the striking piston. The contrivance in consideration preferably consists of a non-return valve loaded by a certain force in an opening located at or in the end wall of the striking piston cylinder defining the outer cylinder space.

Air is generally introduced on the side of the auxiliary piston facing the engine cylinder, that is to say, into the inner cylinder chamber or space of the striking piston cylinder, and the space on this side of the auxiliary piston mostly serves as a compressing space for air, which is used to scavenge the bore hole in connection with rock drilling machines. In breaking machines, the compressed ice:

air is released to the surroundings. However, an air cushion is enclosed within said cylinder space in both types of machines, said air cushion aiding toward absorbing the shock at the return of the striking piston and having for its purpose to prevent the striking piston from striking against the end Wall. At the powerful return setting in at the explosion in the gas cushion on the inside of the striking piston the air cushion does not suflice, the striking piston striking in spite of the same against the end wall of the cylinder. The risk for this is reduced considerably by the pressure restricting contrivance on the outside of the striking piston. A further improvement is obtainable by the fact that the cylinder space on this side of the piston is relieved of pressure, in a certain degree at least, by a further valve, when the striking piston approaches its inner (upper) position. This valve may be constructed as a non-return valve, which is loaded by a relatively weak spring and opens to release pressure medium on the outside of the striking piston toward the end of the return stroke of the same. Hereby the back pressure from the pressure medium is also reduced to a suitable value during the working stroke of the piston. Said slightly loaded non-return valve may be constructed so that the pressure medium is released to the atmosphere, or, it may be connected to a channel conveying the pressurized medium to the drilling tool for the purpose of scavenging the bore hole should the machine be adapted for drilling.

An example of applying the invention is illustrated in the accompanying drawing, in which Fig. 1 shows an axial section through a rock drilling machine and Fig. 2 is an axial part section illustrating an air inlet valve.

As will appear from the drawing, the machine is provided with a freely running striking piston 10, which is formed as a differential piston having a piston member 14 of a small diameter fitted into an engine cylinder 12 and an auxiliary piston 16 of a larger diameter. The auxiliary piston is movable in a striking piston cylinder 18, which forms a downward continuation of the engine cylinder 12. The combustion chamber 20 of the engine is defined at the bottom by the piston member 14 of the striking piston and at the top by the engine piston 22. The striking piston continues downwardly by a piston rod 24, which is guided in a tubular guide 26 in a cylinder cover 28 limiting the cylinder space of the striking piston cylinder outwardly (downwardly). In an inward direction the cylinder space is limited by an end wall 30 forming a transition between the engine cylinder and the striking piston cylinder. The lower end of the piston rod 24 is adapted during the work of the machine, when the striking piston moves back and forth in the cylinder, to strike against the upper end of the tool 32, which is seated in a guide sleeve 34. This guide sleeve is seated in a sleeve 36, which is retained at the lower end of a casing 33. Provided in this casing is a rotating mechanism 40a, 40b, which is used when the machine is adapted for drilling, but which is inoperative when the machine is adapted for breaking work.

The cylinder space 42 of the striking piston cylinder on the side of the auxiliary piston 16 remote from the engine cylinder communicates with the cylinder space 24 through a channel 44 having a non-return valve 36 therein, in which cylinder space 42 a gas cushion is to form for the purpose of returning the striking piston. The channel 44 opens through a port 43 into the cylinder space 42 at some distance from the end wall formed by the cover 28. On the side of the auxiliary piston 16 facing the engine cylinder, the cylinder space 5d cornmunicates with the atmosphere through a port 51 and a channel 53 provided with an inlet non-return valve in the form of a spring flap 55 cooperating with a seat 57 as shown in Fig. 2 so that air will be sucked into said I cylinder space.

In order that too high pressures and any explosions of vaporized oil caused thereby shall be prevented from ensuing in the cylinder space 42, the latter is connected with the atmosphere through a non-return valve 52 with an inlet 54 and outlet passages 56. The valve body of the non-return valve is kept in its closed position by means of a spring 58 loading the same with so great a force that the non-return valve will open only if the pressure in the cylinder space 42 exceeds the pressure normally required in the gas cushion to return the striking piston. The inlet port 54 of the valve is located in the cylinder wall immediately adjacent the end wall 28 but could also be arranged in the end wall.

The striking piston cylinder communicates with the atmosphere through a further non-return valve designated by 60 and having its inlet port 62 in the cylinder wall in the propinquity of but at a certain distance from the inner (upper) end wall 30. This valve is loaded by a relatively weak spring 64, which opens for the release of pressure medium from the space 42 through its outlet passages 66 when the piston 16 has moved past its inlet port 62 during the return stroke of the piston. Hereby the space 42 will be relieved of pressure, so that the back pressure from the gas cushion therein does not become too great during the working stroke of the striking piston.

The mode of operation of the arrangement described is broadly as follows:

When the striking piston is thrown outwardly in known manner upon ignition and explosion in the cylinder space 20 of the engine cylinder, gas entering the cylinder space 42 through the valve 46 is being compressed. If the pressure then becomes too high in this space (which might occur when the striking piston approaches its extreme position), the valve 52 will open to release some of the gas, so that the pressure is reduced to a suitable value. In the propinquity of its extreme position the piston rod 24 of the striking piston then strikes against the neck of the tool 32 with a blow, which is not reduced by any too high back pressure in the cylinder space 42. When the striking piston is then thrown back again toward its inner extreme position, air is being compressed, such air having in the meantime entered the cylinder space 50 through the air inlet valve (not shown in the drawing). If the air pressure become too high, before the auxiliary piston 16 has moved past the inlet port 62 of the nonreturn valve 60, the latter is caused to open to release some of the air to the environment. When the auxiliary piston 16 has moved past the inlet port 62 of the nonreturn valve 60, the latter is caused to open to release some of the air to the environment. When the auxiliary piston 16 has moved past the inlet port 62 during its return stroke the pressure medium will be released from the space 42 on the lower side thereof, so that the back pressure does not become too high at the next following working stroke but assumes a suitable value. This value may be adjusted by suitably adapting the loading of the valve 60, that is to say the strength of the spring 64. An air cushion (50) is then enclosed in the space 50 on the upper side of the auxiliary piston, whereby the auxiliary piston is prevented from striking against the end wall 30, or whereby any blow against this wall is mitigated.

The invention is not limited to the example of embodiment shown. It may, for instance, also be applied in such machines wherein the striking piston is returned with the aid of compressed air, the channel 44 being then connected to a compressor instead of to the engine cylinder.

What I claim is:

1. An explosion percussion machine comprising a cylinder, a power piston in said cylinder, a free floating percussion piston defining together with said power piston, an explosion chamber in the cylinder, said percussion piston comprising an auxiliary piston defining at an outer side thereof a gas cushion chamber with an inlet for a pressure medium for returning the percussion piston upon a working stroke, the wall of said gas cushion chamber defining an opening located at an end wall of the cylinder, a non-return valve in said opening, said valve comprisin g loading means capable of keeping the valve in a closed position for pressures below a maximum value higher than the pressure normally required in the gas cushion chamber to return the percussion piston but being capable of opening to the atmosphere at pressures in the gas cushion chamber exceeding said maximum value.

2. An explosion percussion machine comprising a cylinder, a power piston in said cylinder, a free floating percussion piston defining together with said power piston an explosion chamber in the cylinder, said percussion piston comprising an auxiliary piston in an end portion of the cylinder, a cylinder cover forming an outer end wall of said cylinder end portion and defining together with said auxiliary piston a gas cushion chamber with an inlet for pressure medium for returning the percussion piston on a working stroke, the wall of the gas cushion chamber defining an outlet passage with a port at said cylinder cover, and a non-return valve in said outlet passage, said valve comprising loading means capable of keeping the valve in a closed position for pressures below a maximum value higher than the pressure normally required in the gas cushion chamber to return the percussion piston but being capable of opening to the atmosphere at pressures in the gas cushion chamber exceeding said maximum value.

3. An explosion percussion machine comprising a cylinder, a power piston and a free percussion piston in the cylinder, said pistons defining between themselves an explosion chamber in the cylinder, the percussion piston being a differential piston with its large portion in an end part of the cylinder between an inner end wall and an outer end wall of said cylinder part, a cylinder cover defining said outer end wall and confining a gas cushion chamber together with said large piston portion in said end part of the cylinder, means to admit gas to the gas cushion chamber, an air chamber being confined between said inner end wall and the large piston portion, a nonreturn valve in an outlet passage at said cover, said valve comprising loading means capable of keeping the valve in a closed position for pressures below a maximum value higher than the pressure normally required in the gas cushion chamber to return the percussion piston but being capable of opening to the atmosphere at pressures in the gas cushion chamber exceeding said maximum value, and a further non-return valve in an outlet passage in the Wall of said cylinder end part near the inner end wall thereof but at a distance therefrom, said latter outlet passage leading to the atmosphere to release air from said air chamber at a predetermined pressure lower than the maximum pressure in the gas cushion chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,920,765 Rasch Aug. '1, 1933 2,684,055 Bergman July 20, 1954 FOREIGN PATENTS 773,312 France Aug. 27, 1934 707,255 Great Britain Apr. 14, 1954 

